1. Field of the Invention
This invention relates to a process and apparatus for removing chemical contaminants from soil, and more particularly to a process and apparatus in which vacuum extraction is used to remove contaminants in both liquid and gaseous phases. The invention relates to a process and apparatus for (1) the removal from soil of volatile organic compounds, (2) continuous and simultaneous remediation of the treated soil and (3) the removal of ground water and suspended or dissolved contaminants.
Contaminants may exist in subsurface soil in the liquid or vapor phase as discrete substances and mixed with and/or dissolved in ground water and soil gases. Such contaminants may be found and dealt with in accordance with this invention in the vadose (unsaturated) zone found between the surface of the earth and the water table, at the interface between the vadose zone and the water table, and in the saturated zone below the water table.
2. Description of the Prior Art
At many industrial and commercial facilities and at waste handling and disposal sites, soil and ground water are contaminated with suspended or water-soluble chemicals, or both.
A variety of techniques have been used for removal of soil contaminants and remediation of affected soil. One common technique involves the excavation and off-site treatment of the soil. Another technique involves saturating the contaminated soil with water in situ, causing the contaminants to be slowly leached from the soil by the water. The contaminated water can then be removed.
Techniques have also been proposed for removing volatile organic contaminants from soil by vacuum extraction. For example, in U.S. Pat. No. 4,323,122, it was proposed that a vacuum be applied in a borehole at the level of the water table, the assumption being that a contaminant such as gasoline, which is lighter than water for example, would float on the water table and present a layer which could be drawn off by vacuum applied to the liquid at or around that level.
Others have suggested the possibility of venting soil above the water table (i.e., in the vadose zone) to cause vaporization of the contaminant in the soil, and then drawing off the contaminant in the vapor phase. Thus, conventional vacuum extraction systems are designed to clean the vadose zone by applying vacuum to draw air through the soil through wells having screening which does not extend below the water table. Ground water requiring treatment is in such processes conventionally removed by pumping from separate conventional water wells. In situations in which water does flow into vacuum extraction wells, it has been suggested that a second, liquid phase pump be placed either in the well or at the surface to remove the water through a second conduit. Thus, conventionally, water wells separate and apart from vacuum extraction wells may be required at a given site, and water pumps in addition to vacuum generation devices may be employed. In accordance with the present invention, which exploits two phase vacuum extraction, a single vacuum device removes contaminants in both the water and the soil gases by way of a single conduit formed by the well casing.